Persistent inhibitory circuit defects and disrupted social behaviour following in utero exogenous cannabinoid exposure.

Placental transfer of Δ9-tetrahydrocannabinol (THC) during pregnancy has the potential to interfere with endogenous cannabinoid (CB) regulation of fetal nervous system development in utero. Here we examined the effect of maternal CB intake on mouse hippocampal interneurons largely focusing on cholecystokinin-expressing interneurons (CCK-INTs), a prominent CB subtype-1 receptor (CB1R) expressing neuronal population throughout development. Maternal treatment with THC or the synthetic CB1R agonist WIN55,212-2 (WIN) produced a significant loss of CCK-INTs in the offspring. Further, residual CCK-INTs in animals prenatally treated with WIN displayed decreased dendritic complexity. Consistent with these anatomical deficits, pups born to CB-treated dams exhibited compromised CCK-INT-mediated feedforward and feedback inhibition. Moreover, pups exposed to WIN in utero lacked constitutive CB1R-mediated suppression of inhibition from residual CCK-INTs and displayed altered social behavior. Our findings add to a growing list of potential cell/circuit underpinnings that may underlie cognitive impairments in offspring of mothers that abuse marijuana during pregnancy.

PDZ proteins interacting with C-terminal GluR2/3 are involved in a PKC-dependent regulation of AMPA receptors at hippocampal synapses.

We investigated the role of PDZ proteins (GRIP, ABP, and PICK1) interacting with the C-terminal GluR2 by infusing a ct-GluR2 peptide ("pep2-SVKI") into CA1 pyramidal neurons in hippocampal slices using whole-cell recordings. Pep2-SVKI, but not a control or PICK1 selective peptide, caused AMPAR-mediated EPSC amplitude to increase in approximately one-third of control neurons and in most neurons following the prior induction of LTD. Pep2-SVKI also blocked LTD; however, this occurred in all neurons. A PKC inhibitor prevented these effects of pep2-SVKI on synaptic transmission and LTD. We propose a model in which the maintenance of LTD involves the binding of AMPARs to PDZ proteins to prevent their reinsertion. We also present evidence that PKC regulates AMPAR reinsertion during dedepression.

Hippocampal LTD expression involves a pool of AMPARs regulated by the NSF-GluR2 interaction.

We investigated whether the interaction between the N-ethyl-maleimide-sensitive fusion protein (NSF) and the AMPA receptor (AMPAR) subunit GluR2 is involved in synaptic plasticity in the CA1 region of the hippocampus. Blockade of the NSF-GluR2 interaction by a specific peptide (pep2m) introduced into neurons prevented homosynaptic, de novo long-term depression (LTD). Moreover, saturation of LTD prevented the pep2m-induced reduction in AMPAR-mediated excitatory postsynaptic currents (EPSCs). Minimal stimulation experiments indicated that both pep2m action and LTD were due to changes in quantal size and quantal content but were not associated with changes in AMPAR single-channel conductance or EPSC kinetics. These results suggest that there is a pool of AMPARs dependent on the NSF-GluR2 interaction and that LTD expression involves the removal of these receptors from synapses.

Afferent specific role of NMDA receptors for the circuit integration of hippocampal neurogliaform cells.

Appropriate integration of GABAergic interneurons into nascent cortical circuits is critical for ensuring normal information processing within the brain. Network and cognitive deficits associated with neurological disorders, such as schizophrenia, that result from NMDA receptor-hypofunction have been mainly attributed to dysfunction of parvalbumin-expressing interneurons that paradoxically express low levels of synaptic NMDA receptors. Here, we reveal that throughout postnatal development, thalamic, and entorhinal cortical inputs onto hippocampal neurogliaform cells are characterized by a large NMDA receptor-mediated component. This NMDA receptor-signaling is prerequisite for developmental programs ultimately responsible for the appropriate long-range AMPAR-mediated recruitment of neurogliaform cells. In contrast, AMPAR-mediated input at local Schaffer-collateral synapses on neurogliaform cells remains normal following NMDA receptor-ablation. These afferent specific deficits potentially impact neurogliaform cell mediated inhibition within the hippocampus and our findings reveal circuit loci implicating this relatively understudied interneuron subtype in the etiology of neurodevelopmental disorders characterized by NMDA receptor-hypofunction.Proper brain function depends on the correct assembly of excitatory and inhibitory neurons into neural circuits. Here the authors show that during early postnatal development in mice, NMDAR signaling via activity of long-range synaptic inputs onto neurogliaform cells is required for their appropriate integration into the hippocampal circuitry.

Kainate receptors: subunits, synaptic localization and function.

Although it is well established that kainate receptors constitute an entirely separate group of proteins from AMPA receptors, their physiological functions remain unclear. The molecular cloning of subunits that form kainate receptors and the ability to study recombinant receptors is leading to an increased understanding of their functional properties. Furthermore, the development of kainate receptor-selective agonists and antagonists over the past few years is now allowing the physiological roles of these receptors and, in some cases, specific subunits to be investigated. As a consequence, the synaptic activation of postsynaptic kainate receptors and the presence of presynaptic kainate receptors that serve to regulate excitatory and inhibitory synaptic transmission have been described, and will be discussed in this article by Ramesh Chittajallu, Steven Braithwaite, Vernon Clarke and Jeremy Henley.

Ca2+ and synaptic plasticity.

A major effort in neuroscience is directed towards understanding the roles of Ca2+ signalling in the induction of synaptic plasticity. Here, we summarize the evidence concerning Ca2+ signalling, paying particular attention to CA1 excitatory synapses, and its relationship to the induction of long-term potentiation and long-term depression. We discuss the ways in which synaptic activation can elevate Ca2+ postsynaptically and how dendritic spines may act as a Ca2+ compartment which can both isolate and integrate Ca2+ signals.

NG2-positive cells in the mouse white and grey matter display distinct physiological properties.

Cells that express the NG2 proteoglycan are the largest proliferative progenitor population in the postnatal central nervous system (CNS). Although this entire population has long been considered to be oligodendrocyte progenitors, numerous NG2(+) cells are present in the cerebral cortex, where relatively little myelination occurs, and also persist long after myelination is complete in the CNS. Several studies have alluded to the presence of distinct NG2(+) cell subtypes based on marker expression, but no experimentally derived hypotheses about the physiological role of these subtypes has been proposed. In the current study, whole-cell patch-clamp data from acutely isolated slices demonstrate that subcortical white matter and cortical NG2(+) cells display distinct membrane properties in addition to possessing differing K(+)- and Na(+)-channel expression profiles. A striking observation is that a subpopulation of cortical, but not white matter NG2(+) cells, elicit depolarization-induced spikes that are akin to immature action potentials. Our data demonstrate that a population of cortical NG2(+) cells display physiological properties that differ from their white matter counterparts.

Effect of Helicobacter pylori on parietal cell sensitivity to pentagastrin in duodenal ulcer subjects.

We have investigated the possibility that hypergastrinaemia in chronic Helicobacter pylori infection is a compensatory response to reduced parietal cell sensitivity to gastrin. The acid response to 45-min infusions of pentagastrin at sequential doses (micrograms/kg/h) of 0, 0.031, 0.062, 0.124, and 0.6 was compared before and 1 month after eradication of H. pylori in eight duodenal ulcer patients. The median acid outputs (mmol/h) with the respective infusions were 5.0, 7.5, 26.5, 30.8, and 37.0 when H. pylori-positive and similar at 4.5, 7.1, 22.7, 28, and 31.5 when H. pylori-negative. The median estimated dose of pentagastrin required to produce 50% maximal response (D50) was similar before (0.060 micrograms/kg/h) and after (0.057 micrograms/kg/h) eradication of H. pylori. The median estimated maximal response to pentagastrin (mmol/h) was also similar before (39.2) and after (32.3) treatment. The median basal gastrin concentration was 48 ng/l (range, 22-77) before treatment and fell to 33 ng/l (range, 8-37) after eradication of H. pylori (p = 0.03). These findings show that the parietal cell sensitivity to pentagastrin is unaffected by chronic H. pylori infection in duodenal ulcer subjects and that the hypergastrinaemia cannot be attributed to the bacterium inhibiting parietal cell function.

Effect of increasing Helicobacter pylori ammonia production by urea infusion on plasma gastrin concentrations.

It has been proposed that the hypergastrinaemia in subjects with Helicobacter pylori infection is caused by the action of the ammonia produced by the organism's urease activity on the antral G cells. To investigate this hypothesis we examined the effect on plasma gastrin of increasing the bacterium's ammonia production by infusing urea intragastrically to eight H pylori positive duodenal ulcer patients. After a 60 minute control intragastric infusion of dextrose solution at 2 ml/minute, a similar infusion containing urea (50 mmol/l) was continued for four hours. During the urea infusion, the median gastric juice urea concentration rose from 1.1 mmol/l (range 0.3-1.6) to 15.5 mmol/l (range 7.9-21.3) and this resulted in an increase in the ammonium concentration from 2.3 mmol/l (range 1.3-5.9) to 6.1 mmol/l (range 4.2-11.9) (p less than 0.01). This appreciable rise in ammonia production did not result in any change in the plasma gastrin concentration. The experiment was repeated one month after eradication of H pylori, at which time the median basal gastrin was 20 ng/l (range 15-25), significantly less than the value before eradication (30 ng/l range 15-60) (p less than 0.05). On this occasion, the gastric juice ammonium concentration was considerably reduced at 0.4 mmol/l (range 0.1-0.9) and the urea infusion did not raise the ammonium concentration or change the plasma gastrin concentration. In conclusion, augmenting H pylori ammonia production does not cause any early change in plasma gastrin.

Helicobacter pylori-related hypergastrinaemia is not due to elevated antral surface pH. Studies with antral alkalinisation.

It has been postulated that Helicobacter pylori-related hypergastrinaemia is due to bacterial ammonia raising antral surface pH and thus preventing acid inhibition of gastrin release. If true, the infection should not alter gastrin release at neutral intragastric pH. To test this, we have studied basal and meal-stimulated gastrin at uncontrolled pH and at pH greater than 6 in duodenal ulcer patients before and after eradication of H. pylori. The median integrated gastrin response to the meal alone was 2525 ng/l.min (range, 550-8725) before and 725 ng/l.min (range, 250-2925) after eradication of H. pylori (p less than 0.01). The corresponding values when intragastric pH was maintained above 6 were 3700 ng/l.min (range, 1900-14,100) and 1400 ng/l.min (range, 400-3400) (p less than 0.01). The median reduction in gastrin after eradication of H. pylori was thus similar when the meal was taken at uncontrolled pH (61%; range, 0-97%) and at pH greater than 6 (69%; range, 36-89%). Likewise, 5 h of gastric alkalinisation did not cause the basal gastrin values when H. pylori was eradicated to increase to those observed when H. pylori was present. These findings indicate that the hypergastrinaemia is not due to elevated antral surface pH.

Effect of Helicobacter pylori on serum pepsinogen I and plasma gastrin in duodenal ulcer patients.

Duodenal ulcer patients have increased serum pepsinogen I (PGI) concentrations and an increased prevalence of Helicobacter pylori infection. We have examined the effect of eradicating the infection on PGI. In 12 duodenal ulcer patients in whom H. pylori was successfully eradicated, the median basal PGI was 90 ng/ml (range, 37-252) before treatment and fell to 74 ng/ml (28-197) 1 month after treatment (p less than 0.01). In 12 patients in whom therapy failed to eradicate the infection, the PGI was 87 ng/ml (35-128) before treatment and remained unchanged at 83 ng/ml (36-119) 1 month after treatment. In the group with successful eradication the median basal plasma gastrin was 43 ng/l (15-95) before treatment and fell to 30 ng/l (17-75) 1 month after treatment (p less than 0.003), but there was no change in the corresponding values in the group without eradication (55 ng/l; range, 25-120, and 45 ng/l; range, 5-175; p = 0.9). In conclusion, eradication of H. pylori results in a fall in PGI and plasma gastrin, and these changes are not due merely to the anti-H. pylori drugs themselves or to discontinuation of previous ulcer therapy.

Is Helicobacter pylori associated hypergastrinaemia due to the bacterium's urease activity or the antral gastritis?

Eradication of Helicobacter pylori is associated with a fall in serum gastrin but the way in which the infection raises the serum gastrin concentration is not clear. It may be related to the ammonia produced by the bacterium's urease stimulating gastrin release by the antral G cells. Alternatively, the antral gastritis induced by the infection may modify the regulation of gastrin release. We have examined serum gastrin in 10 patients before and 24 hours after starting triple anti-H pylori treatment consisting of tripotassium dicitrato bismuthate 120 mg four times daily, metronidazole 400 mg three times daily, and amoxycillin 500 mg three times daily. The urease activity, assessed by the 20 minute value of the 14C-urea breath test, fell from a median of 176 (range 116-504) kg% dose/mmol CO2 x 100 pretreatment to 5 (2-15) at 24 hours (p less than 0.005). The median antral gastritis score was 6 (4-6) pretreatment and fell to 3 (2-5) at 24 hours (p less than 0.02), and this was due to resolution of the polymorphonuclear component. Despite this complete suppression of bacterial urease activity and partial resolution of antral gastritis the median basal gastrin concentration remained unchanged, being 57 ng/l (45-77) pretreatment and 59 ng/l (45-80) at 24 hours and the median integrated gastrin response to a standardised meal was also unaltered, being 4265 ng/l/min (range 1975-8350) and 4272 ng/l/min (range 2075-6495) respectively. These findings do not support a causal association between H pylori urease activity and hypergastrinaemia and show rapid improvement of antral gastritis after starting anti-H pylori treatment.

Regulation of glutamate release by presynaptic kainate receptors in the hippocampus.

Most reported actions of kainate are mediated by AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors. Here we report that, unlike AMPA which stimulates, kainate elicits a dose-dependent decrease in L-glutamate release from rat hippocampal synaptosomes and also depresses glutamatergic synaptic transmission. Brief exposure to kainate inhibited Ca(2+)-dependent [3H]L-glutamate release by up to 80%. Inhibition was reversed by kainate antagonists but not by the AMPA-selective non-competitive antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466). A corresponding reversible kainate-evoked depression of NMDA (N-methyl-D-aspartate) receptor-mediated excitatory postsynaptic currents (e.p.s.cs) was observed when AMPA receptors were blocked by GYKI 52466. The synaptic depression was preceded by a brief period of enhanced release and a small inward current was also observed. The effects of kainate were unaffected by metabotropic glutamate (mGlu), GABAA, GABAB, glycine and adenosine receptor antagonists. These results indicate that glutamate release can be modulated directly by kainate autoreceptors.

Detection of Helicobacter pylori infection of the gastric mucosa by measurement of gastric aspirate ammonium and urea concentrations.

Helicobacter pylori possesses unusually high urease activity that lowers the urea concentration and raises the ammonium concentration of the gastric juice in infected people. The value of measuring urea and ammonium concentrations in gastric juice obtained during upper gastrointestinal endoscopy as a means of diagnosing the presence and eradication of the infection was assessed. Twenty four subjects with the infection and 14 in whom it had been eradicated were examined. Their H pylori status was confirmed by antral biopsy and 14C urea breath test. The median (range) gastric juice urea concentration in infected subjects was 0.8 mmol/l (0.5-2.9 mmol/l), which was lower than that in the uninfected subjects (2.1 mmol/l (1.0-3.7 mmol/l)) (p less than 0.001). The median gastric juice ammonium concentration in infected subjects was 3.4 mmol/l (1.0-13.0 mmol/l), which was higher than that in the uninfected subjects (0.64 mmol/l (0.02-1.4 mmol/l)) (p less than 0.001). Though the two groups overlapped in respect of their urea and ammonium concentrations, they were completely different when the urea: ammonium ratios were calculated--the ratios ranged from 0.04-0.7 (median 0.26) and from 1.1-113 (median 3.4) in infected and uninfected subjects respectively (p less than 0.001). Treatment with H2 antagonists did not change the concentrations of urea and ammonium or their ratio in gastric juice. Measurement of the urea: ammonium ratio in aspirated gastric juice obtained during routine upper gastrointestinal endoscopy may provide a rapid method of detecting H pylori infection and of confirming its eradication.

Effect of inhibition of Helicobacter pylori urease activity by acetohydroxamic acid on serum gastrin in duodenal ulcer subjects.

The mechanism of the hypergastrinaemia associated with Helicobacter pylori infection is unknown. It may be an effect of the ammonia produced by the bacterium near the antral epithelial surface. We have examined the effect on serum gastrin of inhibiting H pylori urease activity with acetohydroxamic acid in six duodenal ulcer patients. On day 1 the fasted patients received placebo tablets at 8 am, a peptide meal at 10 am, and a 14C urea breath test at 11.30 am. The next day 750 mg acetohydroxamic acid was administered orally in place of the placebo. The median (range) 30 minute breath test value (dose/mmol CO2 X kg body wt X 100) was 152 (111-335) on day 1, but only 22 (14-95) the next day (p less than 0.03). Further studies performed in one subject confirmed that acetohydroxamic acid lowered the ammonium concentration and raised the urea concentration in gastric juice. The inhibition of urease activity and ammonia production did not result in a fall in the basal gastrin concentration or in the median integrated gastrin response to the peptide meal, which was 78 ng/1.h (range 21-222) on day 1 and 79 ng/1.h (33-207) the next day. Ten days after acetohydroxamic acid, the urea breath test values were similar to those before treatment. This study shows that the raised gastrin concentration in patients with H pylori infection is not directly related to the organism's urease activity. It also shows that temporary suppression of H pylori urease activity does not clear the infection.

Helicobacter pylori related hypergastrinaemia is the result of a selective increase in gastrin 17.

Helicobacter pylori infection increases the serum concentration of gastrin, and this may be one of the mechanisms by which it predisposes to duodenal ulceration. Different forms of circulating gastrin were studied both basally and postprandially in 13 duodenal ulcer patients before and one month after eradication of H pylori. Three antisera that are specific for particular regions of the gastrin molecules were used. Gel chromatography indicated that > 90% of the circulating gastrin consisted of gastrin (G) 17 and G34 both before and after eradicating the infection. The basal median total immunoreactive gastrin concentration fell from 26 pmol/l (range 11-43) to 19 pmol/l (8-39) (p < 0.05), entirely because of a fall in G17 from 6 pmol/l (< 2.4-25) to < 2.4 pmol/l (< 2.4-23) (p < 0.001). The median (range) basal G34 values were similar before (15 pmol (2-36)) and after (10 pmol (2-30)) eradication. The median total immunoreactive gastrin concentration determined 20 minutes postprandially fell from 59 pmol/l (38-114) to 33 pmol/l (19-88) (p < 0.005), and again this was entirely the result of a fall in G17 from 43 pmol/l (9-95) to 17 pmol/l (< 2.4-52) (p < 0.001). The median postprandial G34 values were similar before (13 pmol/l, range 6-42) and after (15 pmol/l, range 6-30) eradication. Eating stimulated a noticeable rise in G17 but little change in G34, both in the presence and absence of H pylori. The finding that H pylori infection selectively increases G17 explains why the infection causes mainly postprandial hypergastrinaemia. G17 is increased selectively because H pylori predominantly affects the antral mucosa which is the main source of G17 whereas G34 is mainly duodenal in origin. This study also indicates that the increased concentration of gastrin in H pylori infection is the result of an increase in one of the main biologically active forms of the hormone.

Helicobacter pylori infection and abnormalities of acid secretion in patients with duodenal ulcer disease.

BACKGROUND & AIMS: The mechanism by which Helicobacter pylori predisposes to duodenal ulcers (DUs) remains unclear. The aim of this study was to investigate the effect of the infection on acid secretion. METHODS: Acid output was examined basally and in response to gastrin-releasing peptide (GRP) and gastrin in healthy volunteers with and without H. pylori infection and in patients with DUs before and after eradication of the infection. RESULTS: Compared with H. pylori-negative healthy volunteers, patients with DUs with H. pylori had the following abnormalities of acid secretion: (1) threefold increase in basal acid output, (2) sixfold increase in acid response to GRP, (3) increased maximal acid response to exogenous gastrin, (4) increased ratio of basal acid output to maximal gastrin-stimulated output, and (5) increased ratio of maximal GRP-stimulated acid output to maximal gastrin-stimulated output. All of these abnormalities resolved fully after H. pylori eradication except for increased maximal acid output to gastrin, which was unchanged. Infected healthy volunteers showed a threefold increase in acid response to GRP that resolved after eradication of H. pylori infection. CONCLUSIONS: These disturbances in acid secretion caused by H. pylori infection are consistent with impaired inhibitory control and are likely to be relevant to the mechanism by which the infection predisposes to DU.

Regulation of Kv1 subunit expression in oligodendrocyte progenitor cells and their role in G1/S phase progression of the cell cycle.

Proliferative oligodendrocyte progenitor cells (OPs) express large, delayed outward-rectifying K(+) currents (I(K)), whereas nondividing immature and mature oligodendrocytes display much smaller I(K). Here, we show that up-regulation of I(K) occurs in G(1) phase of the cell cycle in purified cultured OPs and is the result of an RNA synthesis-dependent, selective increase of the K(+) channel subunit proteins Kv1.3 and Kv1.5. In oligodendrocyte cells acutely isolated from developing rat brain, a decrease of cyclin D expression is observed as these cells mature along their lineage. This is accompanied by a decrease in Kv1.3 and Kv1.5 subunit expression, suggesting a role for these subunits in the proliferative potential of OPs in situ. I(K) expressed in OPs in subventricular zone and developing white matter in acutely isolated slice preparations were selectively blocked by antagonists of Kv1.3, illustrating the functional presence of this subunit in situ. Interestingly, Kv1.3 block inhibited S-phase entry of both purified OPs in culture and in tissue slice cultures. Thus, we employ both in vitro and in situ experimental approaches to show that (i) RNA-dependent synthesis of Kv1.3 and Kv1.5 subunit proteins occurs in G(1) phase of the OP cell cycle and is responsible for the observed increase in I(K), and (ii) currents through Kv1.3-containing channels play a crucial role in G(1)/S transition of proliferating OPs.